1. Field of the Invention
The present invention relates to an ion implanting apparatus of carrying out ion implanting by irradiating to a substrate ion beam brought out from an ion source having a plurality of filaments, and in particular an improvement of means for controlling beam current of the ion beam brought out from the ion source to be at a predetermined value and an excellent uniformity as well.
2. Description of the Related Art
A conventional example of this kind of ion-implanting apparatus is shown in FIG. 8. This ion implanting apparatus is also called as an ion doping apparatus (or an ion implanting apparatus of non-mass separating type) which directly irradiates to a substrate 14 an ion beam 12 of large area brought out from the ion source 2 as it is, not passing through a mass separator, so as to carry out the ion implanting to the substrate 14. When implanting the ion, if required, the substrate 14 may be mechanically scanned within an area of implanting the ion beam, for example, in directions from an inside to an outside of this FIG. 8 drawn paper. The substrate 14 is such as a glass substrate or semi-conductor substrate.
The ion source 2 is also called as a bucket type ion source (or a multi-polar magnetic field type ion source) which has a plurality of filaments 6 (for example, three) within a plasma production container 4, so that an arc discharge is generated between each filament 6 and the plasma production container 4 to ionize gas of the ion source and generate the plasma 8, and the ion beam 12 is brought out from the plasma 8 by an extension electrode system 10. A magnet for forming multi-polar magnetic field is not illustrated.
To the respective filaments 6, in this example, filament sources 16 are connected, and filament current IF heating the filament 6 can be independently passed from each filament source 16 to each filament 6.
For controlling the beam current of the ion beam 12 brought out from the ion source 2 to be at a predetermined value, this ion implanting apparatus receives a further ion beam 12 and measures the beam current in a plurality of positions within a plane crossing with the ion beam 12. The ion implanting apparatus is provided with a plurality of beam current measuring instruments 18, the number of which is more (for example 24) than the number of the filaments 6 and provided with a control apparatus 20 which demands an average value of the beam current IB measured by the respective beam current measuring instruments 18 and controls increase and decrease by the same amount of the filament currents IF passing to the respective filaments 6 such that the average value approaches to a fixed value.
Each of the beam current measuring instruments 18 is composed of such as Faraday cup, and is disposed, for example, in a straight line within an irradiating area of the ion beam 12. While the ion beam 12 is measured by the beam current measuring instrument 18, the substrate 14 is moved to a place not to interrupt the ion beam 12.
In the ion implanting apparatus, the ratio of the filament current IF passing to the respective filaments 6 is set in advance such that the uniformity of the ion beam 12 is made good, and the ion implanting apparatus is operated.
However, since changing manners of the respective filaments 6 with time passing are ordinarily different one another, if serving the above mentioned control apparatus 20 which increases and decreases by the same amount the filament current IF flowing to the respective filaments 6, there arises a problem that the uniformity of the ion beam 12 is worsened with the time passing of the filaments 6.
JP-A-3-134937 discloses a technology of providing the beam current measuring instruments of the same number as that of the filaments, and controlling the filament current flowing to the respective filaments such that the beam current to be measured by the respective beam current measuring instruments meets the set values.
Although, in this published technology, it seems to be possible to uniform the ion beams by making the respective set values equal one another, actually the control of the filament current flowing to one filament gives influences to plasma density in the vicinity of other filaments, and gives in its turn influence to beam current to be measured by other beam measuring instruments, that is, the controls of the filament current affect one another. If a beam current of one measuring point is controlled to be at a predetermined value, another beam current at another measuring point gets off from the predetermined value, and if trying to control this off beam current to be at the predetermined value, that beam current controlled to have been at the one measuring point gets off from the predetermined value. This is a serious problem that the control causes hunting and does not converge.
There is further proposed an (PJ-A-11-123973), in which the filament current is controlled to pass to the filaments in accordance with a plurality of beam current measuring instruments and the beam current measured thereby, and a control apparatus is equipped which performs a current value control routine and a uniformity control routine at least once respectively. The ion implanting apparatus prevents deterioration of the uniformity of the ion beam due to change of the filaments by time passing so as to control the beam current of the ion beam to be at the predetermined value and the excellent uniformity as well. One example thereof will be explained with reference to FIGS. 15 to 20.
The ion implanting apparatus illustrated in FIG. 5 is also called as the ion doping apparatus (or the ion implanting apparatus of non-mass separating type) which directly irradiates to the substrate 14 the ion beam 12 of large width brought out from the ion source 2 as it is, not passing through the mass separator, so as to carry out the ion implanting to the substrate.
The substrate 14 is supported on a substrate holder 13 which is somewhat larger than the substrate 14, and both are scanned reciprocally in a direction of arrow D within the irradiating area of an ion beam 12 brought out from the ion source 2 by means of a holder scanning mechanism 15.
The substrate holder 13 and the substrate 14 are, for example, rectangular (square or rectangle) as shown in FIG. 16. The plane shape of the ion beam 12 is, for example, rectangular as shown in FIG. 16.
The ion source 2 is also called as the bucket type ion source (or the multi-polar magnetic field type ion source) which has a plurality of filaments 6 (for example, three) within the plasma production container 4, so that an arc discharge is generated between each filament 6 and the plasma production container 4 to ionize gas of the ion source and generate the plasma 8, and the ion beam 12 is brought out from the plasma 8 by the extension electrode system 10. The magnet for forming multi-polar magnetic field is not illustrated.
To the respective filaments 6, in this example, the filament sources 16 are connected, and the filament current IF heating the filament 6 can be independently passed from each filament source to each filament 6.
For controlling the beam current of the ion beam 12 brought out from the ion source 2 to be at the predetermined value, this ion implanting apparatus further receives the ion beam 12 and measures the beam current in a plurality of positions at a downstream of the scanning area of the substrate holder 13. The ion implanting apparatus is provided with a plurality of beam current measuring instruments 18, the number of which is more (for example 24) than the number of the filaments 6 and provided with the control apparatus 20 which controls the filament current IF to be passed to the respective filaments 6 from the respective filament sources 16 in accordance with the beam current IB measured by the respective beam current measuring instruments 18.
Each of the beam current measuring instruments 18 is, as shown in FIG. 16, disposed within an irradiating area of the ion beam 12 and at the downstream of the scanning area of the substrate holder 13, for example, in a straight line.
The control apparatus 20 repeats, as shown in FIG. 17, a current value control routine (step 230) and a uniformity control routine (step 231) at least once respectively.
One example of the current value control routines is illustrated in FIG. 18. Profiles of the beam before and after controls are schematically illustrated in FIG. 20, and explanation hereafter will be also referred to FIG. 20. 1 to 24 of a lateral axis of FIG. 20 show the numbers from the tail end of 24 pieces of the beam current measuring instruments 18.
The beam current of the ion beam 12 is measured by the respective beam current measuring instruments 18 (step 250). Thereby, for example, a beam profile A of FIG. 20 is obtained. An average value AVE of measured all beam current IB is calculated (step 251).
Whether or not this average value AVE is within a stopping range STP for the set value SET is judged (step 252). The stopping range STP is, for example, within xc2x13% of the set value SET. Being within the stopping range STP, an purpose of controlling the average value has been already accomplished, and an operation advances to the uniformity control routine shown in the following.
When the average value AVE is not within the stopping range STP, the operation goes forward to a step 253 for judging whether or not the average value AVE is larger than the set value SET, and if it is larger, the operation goes to a step 254 so as to decrease by a predetermined amount the filament current IF passing to all the filaments 6. If it is smaller, the operation goes to a step 255 so as to increase by a predetermined amount the filament current IF passing to all the filaments 6. The increasing or decreasing amount in this example is determined to be almost the same amount (including xe2x80x9cthe samexe2x80x9d) each other with respect to all of the filaments 6. In accordance with the increase and the decrease of the filament current IF, emission electron amounts from the respective filaments 6 are increased or decreased, whereby the density of the plasmas 8 in the vicinity of the respective filaments 6 is increased or decreased, and the beam current of the ion beam 12 brought out from the range corresponding to the filaments 6 is increased or decreased.
By the above current value control routine, the average value AVE of the beam current of the ion beam 12 brought out from the ion source 2 is controlled to a direction being near the set value SET. Thus, a beam profile B in, for example, FIG. is obtained. Since the uniformity control routine is not yet exercised under this condition, the beam profile B is shaped similarly to the original profile A, and it seems to move the beam profile A in parallel.
Subsequently, the operation goes forward to the above mentioned uniformity control routine. One example is shown in FIG. 19.
Herein, 24 pieces of beam current measuring instruments 18 (measuring points) are divided in the number of the filaments 6, that is, three groups (step 260). Actually, as shown in FIG. 20, Nos. 1 to 8 beam current measuring instruments 18 are a group 1, Nos. 9 to 16 instruments 18 are a group 2, and Nos. 17 to 24 are a group 3.
Among all of the measured values by all of the beam current measuring instruments 18, a maximum value MAX and a minimum MIN are sought (step 261) so as to respectively determine the groups belonging to the maximum value MAX and the groups belonging to the minimum value MIN (step 262). In an example of FIG. 20, the maximum value MAX belongs to the group 1, and the minimum value MIN belongs to the group 3.
The filament current IF flowing to the filament 6 corresponding to the group 1 to which the maximum value MAX belongs is decreased by a predetermined amount (step 263), and the filament current IF flowing to the filaments 6 corresponding to the group 3 to which the minimum value MIN belongs is increased by a predetermined amount (step 264). Thus, the beam current of the group 1 is decreased, and the beam current of the group 3 is increased.
By the uniformity control routine, the beam current of the group 1 to which the maximum value MAX of the beam profile B belongs is decreased, while the beam current of the group 3 to which the minimum value MIN belongs is increased, so that the control is performed in a direction where the uniformity of the beam current is made good. Thus, the beam profile C, for example, shown in FIG. 9 is obtained.
The uniformity of the beam current can be defined by (MAXxe2x88x92MIN)/(MAX+MIN), using, for example, the maximum value MAX and the minimum value MIN of all measured points.
According to this ion implanting apparatus, the control apparatus 20 performs the current value control routine and the uniformity control routine at least once respectively, thereby enabling to prevent deterioration of the uniformity due to the time passing of the filament 6 and control the beam current of the ion beam 12 to be at the predetermined value (i.e., the set value SET) and the excellent uniformity as well.
Further, depending on the 2 step controls of the current value control routine and the uniformity control routine, there does not occur a problem that the control causes hunting and does not converge, differently from the prior art set forth in JP-A-3-134937, and the control may be stable.
However, in the prior art ion implanting apparatus, as shown in FIG. 16, while the substrate holder 13 is scanned to irradiate the ion beam 12 to the substrate 14 for implanting the ion to the substrate 14, the substrate holder 13 interrupts the ion beam 12 to inject the beam current measuring instrument 18, so that the measured value of the beam current IB is not output from the beam current measuring instrument 18, and therefore during implanting the ion to the substrate 14, the control cannot be performed to the current value and the uniformity of the ion beam 12.
Time to be taken for one scanning reciprocation of the substrate holder 13 is relatively short as 3 to 20 seconds, and although for such short period of time, the lowering of the uniformity of the ion beam 12 by difference in time passing of the respective filaments 6 of the ion source may be ignored time, since the current value of the ion beam 12 is changed gradually as time passes by conditions of the plasma 8 in the ion source 2, it is preferable to control the current value of the ion beam 12 also during implanting the ion to the substrate 14, actually while the substrate holder 13 interrupts the beam current measuring instrument 18. In such a manner, it is possible to more precisely control the amount (dose amount) of implanting the ion to the substrate 14.
Accordingly, it is a main object of the invention to improve the ion implanting apparatus as shown in FIG. 8 and control the beam current of the ion beam brought out from the ion source thereof to be at the predetermined value and the excellent uniformity as well.
It is another main object of the invention to further improve the ion implanting apparatus as mentioned above and to provide such an ion implanting apparatus which may control, at the predetermined value, the current value of the ion beam brought out from the ion source while the substrate holder interrupts the beam current measuring instrument.
A one ion implanting apparatus of the invention is characterized by providing
a control apparatus which controls filament current passing to each of filaments from the filament sources in accordance with beam current measured by a plurality of beam current measuring instruments, and performs a current value control routine and a uniformity control routine at least once respectively
said current value control routine for calculating the average value of all beam current measured by the plurality of beam current measuring instruments, and increasing and decreasing the filament current passing to the respective filaments by almost the same amount one another such that the average value comes near to the set value, and
said uniformity control routine for grouping said plurality of beam current measuring instruments into the number of the filaments, seeking for a maximum value and a minimum value from all measured values by all beam current measuring instruments so as to respectively decide groups to which the maximum value and the minimum value belong, decreasing the filament current passing to the filaments corresponding to the group to which the maximum value belongs and increasing the filament current passing to the filaments corresponding to the group to which the minimum value belongs.
By the current value control routine, the control is performed in a direction where the average value of the beam current of the ion beam brought out from the ion source comes near to the set value.
On the other hand, by the uniformity control routine, the beam current of the group to which the maximum value of the beam current belongs is decreased, and the beam current of the group to which the minimum value of the beam current belongs is increased, so that the control is performed in the direction where the uniformity of the beam current is made good.
The control apparatus performs the current value control routine and the uniformity control routine at least once respectively, so that the deterioration of the uniformity with time passing of the filament is prevented, and it is possible to control the beam current of the ion beam to be at the predetermined value and the excellent uniformity as well.
In the uniformity control routine, it is sufficient to demand the difference between the maximum value and the minimum value, divide dimensions in difference into a plurality of steps (for example, large, middle, small), and control to differ the amounts of increasing and decreasing the filament current in response to each of the steps. In such a manner, the larger the difference is, the more increasing and decreasing the filament current is, and the beam current may be rapidly increased and decreased, so that the uniformity of the beam current may be rapidly made good.
In the uniformity routine, when the average value of all beam current measured by the plurality of beam current measuring instruments is placed within a predetermined stopping range with respect to the set value and when this average value is larger than this set value, it is sufficient to prohibit the increasing actuation of the filament current passing to the filaments corresponding to the group to which the minimum value belongs, and prohibit the decreasing actuation of the filament current passing to the filaments corresponding to the group to which the maximum value belongs, when the average value is smaller than the set value. In such a manner, in the uniformity control routine, the average value of the beam current can be exactly restrained from beginning to fluctuate and getting out of the stopping range, so that the beam current can be controlled to be at the set value more steadily and more rapidly.
Such a uniformity control routine may be employed, which groups the plurality of beam current measuring instruments into the number of the filaments, calculates the average value of the measured beam current within the respective groups, decides groups having the maximum average value and the minimum average value, decreases the filament current passing to the filaments corresponding to the group having the maximum average value, and increases the filament current passing to the filaments corresponding to the group having the minimum average value. By employing such a uniformity control routine, even if a few of peculiar values or noises are included in the plurality of beam current measured values by the plurality of beam current measuring instruments, since the control is performed in accordance with the average value per each of groups, beam current can be controlled by suppressing the peculiar values or noises to be low.
In the uniformity control routine, it is sufficient to demand the difference between the maximum average value and the minimum average value, divide dimensions in the difference into a plurality of steps (for example, large, middle, small), and control to differ the amounts of increasing and decreasing the filament current in response to each of the steps. In such a manner, the larger the difference is, the more increasing and decreasing the filament current is, and the beam current may be rapidly increased and decreased, so that the uniformity of the beam current may be rapidly made good.
In the uniformity routine, when the average value of all beam current measured by the plurality of beam current measuring instruments is placed within a predetermined stopping range with respect to the set value and this average value is larger than this set value, it is sufficient to prohibit the increasing actuation of the filament current passing to the filaments corresponding to the group to which the minimum value belongs, and prohibit the decreasing actuation of the filament current passing to the filaments corresponding to the group to which the maximum value belongs, when the average value is smaller than the set value. In such a manner, in the uniformity control routine, the average value of the beam current can be exactly restrained from beginning to fluctuate and getting out of the stopping range, so that the beam current can be controlled to be at the set value more steadily and more rapidly.
Another ion implanting apparatus according to the invention is characterized by providing
a control apparatus which controls filament current passing to the respective filaments from the filament sources in accordance with beam current measured by the beam current measuring instruments, and performs a current value control routine and a uniformity control routine at least once respectively,
said current value control routine for calculating the average value of all beam current measured by the plurality of beam current measuring instruments, and increasing and decreasing the filament current passing to the respective filaments by almost the same amount each other such that the average value comes near to the set value, and
said uniformity control routine for grouping said plurality of beam current measuring instruments into the number of the filaments, respectively calculating the average values of the plurality of beam current measuring instruments into the number of the filaments, deciding one group having the average value of a largest difference with respect to the set values, decreasing the filament current passing to the filaments corresponding to said group when the average value of this group is larger than said set value, and increasing the filament current when the average value is smaller than said average value.
By the current value control routine, the control is performed in a direction where the average value of the beam current of the ion beam brought out from the ion source is near to the set value.
On the other hand, by the uniformity control routine, the beam current of the group having the average value of a largest difference with respect to the set values is increased and decreased, so that the control is performed in a direction where the uniformity of the beam current is made good.
The control apparatus performs the current value control routine and the uniformity control routine at least once respectively, so that the deterioration of the uniformity with time passing of the filaments is prevented, and it is possible to control the beam current of the ion beam to be at the predetermined value and the excellent uniformity as well.
In the uniformity control routine, it is sufficient to demand the difference between the maximum average value and the minimum average value, divide dimensions in the difference into a plurality of steps (for example, large, middle, small), and control to differ the amounts of increasing and decreasing the filament current in response to each of the steps. In such a manner, the larger the difference is, the more increasing and decreasing the filament current is, and the beam current may be rapidly increased and decreased, so that the uniformity of the beam current may be rapidly made good.
The ion implanting apparatus of the invention receives the ion beam brought out from the ion source and measures the beam current thereof. The ion implanting apparatus is disposed outside of the scanning range of the substrate holder and is furnished with a non-shield beam current measuring instrument which is not shielded by the substrate holder during scanning.
Moreover, the ion implanting apparatus according to the invention performs a control before scanning of the substrate and a control during scanning per one reciprocal scanning of the substrate holder,
the control before scanning for repeating at predetermined times the current value control routine and the uniformity control routine before scanning of the substrate holder, and
the control during scanning of the substrate for storing as a target a measured value by the non shield beam current measuring instrument immediately before scanning of the substrate holder and increasing and decreasing filament current passing to the filaments by the same amount such that the measured value by the non shield beam current measuring instrument approaches the target value.
In accordance with the above mentioned structure, before scanning of the substrate holder, similarly to the precedent example, the current value control routine and the uniformity control routine are repeated at the predetermined times (control before scanning) following the beam current measured by a plurality of beam current measuring instruments. It is possible thereby to control the beam current of the ion beam from the ion source to be at the predetermined value and the excellent uniformity as well.
On the other hand, during scanning of the substrate holder, the filament current passing to the respective filaments of the ion source is controlled (control during scanning) such that the measured value by the non shield beam current measuring instrument approaches the target value stored immediately before scanning of the substrate holder.
Accordingly, also while the substrate holder shields the beam current measuring instrument, the beam current value of the ion beam brought out from the ion source can be controlled at the redetermined value.
Since the controls before and during scanning are performed per one reciprocal scanning of the substrate holder, the ion can be implanted to the substrate at the exact beam current value and the ion beam of excellent uniformity.